Edge Turbulence Imaging in the Alcator C-Mod Tokamak
Authors: S.J. Zweben, D.P. Stotler, J.L. Terry, B. LaBombard, M. Greenwald, M. Muterspaugh, C.S. Pitcher, the Alcator C-Mod Group, K. Hallatschek, R.J. Maqueda, B. Rogers, J.L. Lowrance, V.J. Mastrocola, and G.F. Renda
Date of PPPL Report: November 2001
Presented at: the American Physical Society Division of Plasma Physics in Long Beach, CA, October 29 through November 2, 2001. Published in Physics of Plasmas 9 No. 5 (May 2002) 1981-1989.
The 2-D radial vs. poloidal structure of edge turbulence in the Alcator C-Mod tokamak [I.H. Hutchinson, R. Boivin, P.T. Bonoli et al, Nuclear Fusion 41, 1391(2001)] was measured using fast cameras and compared with 3-D numerical simulations of edge plasma turbulence. The main diagnostic is Gas Puff Imaging (GPI), in which the visible Da emission from a localized D2 gas puff is viewed along a local magnetic field line. The observed Da fluctuations have a typical radial and poloidal scale of approximately 1 cm, and often have strong local maxima ("blobs") in the scrape-off layer. The motion of this 2-D structure motion has also been measured using an ultra-fast framing camera with 12 frames taken at 250,000 frames/sec. Numerical simulations produce turbulent structures with roughly similar spatial and temporal scales and transport levels as that observed in the experiment; however, some differences are also noted, perhaps requiring diagnostic improvement and/or additional physics in the numerical model.